This is a proposal to examine the medical, psychiatric, perceptual, and cognitive characteristics of cardiac patients referred for 24-hour continuous ambulatory electrocardiographic (Holter) monitoring because of palpitations and/or dizziness. These are two of the most common presenting complaints in general practice, and are the referral request in 25%-35% of outpatient Holter studies, accounting for $95-$280 million annually. Yet the role of the ambulatory electrocardiogram (ECG) in the clinical evaluation of these patients remains unclear: only a small minority have significant arrhythmias that account for their presenting symptoms, and little else is known about the etiology of their complaints. This study will describe and compare 150 such Holter patients with and without demonstrable arrhythmias ("accurate reporters" and "over-reporters"). An age and sex-matched control group of 75 asymptomatic non-patients will be accrued. Subjects will be examined at the time of the Holter study and again six months later, with self-report questionnaires, structured and semi-structured interviews, and perceptual and cognitive tests. Data will be gathered in several domains: cardiac symptoms, cardiac status, and ECG findings; psychiatric diagnosis, including panic disorder, depressive disorder and somatoform disorder; somatization; life change and life stress; pattern of medical care utilization; and selected perceptual and cognitive characteristics. Two sets of hypotheses will be tested. The first deals with the clinical characteristics of over-reporters, as compared to accurate reporters and controls, including cardiac symptomatology, psychiatric disorder and somatization, life stress, and medical utilization. The prospective follow-up will document the course of the patients' symptoms, the incidence of previously undiagnosed medical and psychiatric disorder, and persistent patterns of medical utilization. The second set of hypotheses predicts that over-reporters are perceptual and cognitive amplifiers of benign, physiological changes in heart rate and rhythm. They will be tested with a somatosensory amplification questionnaire, a heart beat discrimination task, and two cognitive tests of information processing. The findings will improve the clinical evaluation of patients complaining of palpitations and dizziness, and clarify the role of ambulatory ECG monitoring in that evaluation. This work may lead to specific cognitive and educational palliative techniques for cardiac patients who are unduly distressed by these symptoms. The findings will also advance our understanding of somatic amplification and the somatization of psychiatric distress.